Defects in the regulation of retinal and choroidal flow are part of the etiology of diabetic retinopathy, glaucoma, and other vision-threatening disorders, yet the physics and physiology controlling of blood flow to the retina is poorly understood, at least in part because of the limitations of current methods of measuring blood flow. The goal of this research is to quantitatively study the control of flow and the hemodynamics in the choroidal and retinal circulations and their relationships to retinal disease. The hypothesis is that blood flow in the retinal and choroidal circulations is not homogeneous and that increased heterogeneity in blood flow may be an early indicator of dysfunction of the retinal and choroidal circulations. As part of this work simultaneous, continuous and quantitative measurements of tissue perfusion in the choroidal and retinal circulations will be made to allow study of how the retina and choroidal circulations interact in response to physiological conditions. Previous investigations of the role of the vasculature in health and disease have been hampered by the limits of technology. In this project Color Doppler Optical Coherence Tomography (CDOCT), a novel non-invasive imaging technology, will be adapted to measure hemodynamic parameters in the circulations that serve the retina. The specific aims will first address the instrumentation and quantification of blood flow and then validate the results using in-vivo comparison to Laser Doppler Flowmetery, the most commonly used current method of assessing perfusion. The method will then be used in animal experiments to determine the effects of perfusion pressure and blood gasses on the regional distribution of blood flow and local hematocrit in the retinal and choroidal circulations, with and without ganglionic blockade and other maneuvers which act differently on the two circulations.